A 68-year-old man is evaluated in the hospital for new-onset diarrhea. He was admitted 8 d… — USMLE Step 2 CK

A $68$ -year-old man is evaluated in the hospital for new-onset diarrhea. He was admitted $8$ days ago for a chronic obstructive pulmonary disease (COPD) exacerbation and was treated with a $5$ -day course of systemic glucocorticoids and levofloxacin. Over the last $48$ hours, he has had $6$ to $8$ watery bowel movements daily, accompanied by lower abdominal cramping and low-grade fever. Vitals: T $37.9^\circ\text{C}$ ( $100.2^\circ\text{F}$ ), HR $92/\text{min}$ , BP $118/76 \text{ mmHg}$ . Physical examination reveals mild, diffuse abdominal tenderness with normal bowel sounds; there is no rebound tenderness or guarding. Laboratory studies show a leukocyte count of $16,500/\text{mm}^3$ and serum creatinine of $1.1 \text{ mg/dL}$ (baseline $0.9 \text{ mg/dL}$ ). Stool enzyme immunoassay is positive for *Clostridioides difficile* glutamate dehydrogenase antigen and toxins A and B. Which of the following is the most appropriate next step in management?

A
Intravenous vancomycin
B
Oral metronidazole
Oral fidaxomicinAnswer
D
Intravenous piperacillin-tazobactam
E
Oral loperamide

Answer

Oral fidaxomicin

This patient has an initial episode of non-fulminant *Clostridioides difficile* infection (CDI). According to updated clinical guidelines, the preferred first-line treatment for both non-severe and severe initial episodes of CDI is oral fidaxomicin. Oral vancomycin is an acceptable alternative. Fidaxomicin is a narrow-spectrum macrocyclic antibiotic that is minimally absorbed, resulting in high fecal concentrations. It targets *C. difficile* with minimal disruption to the protective normal colonic microbiome, which leads to lower rates of disease recurrence compared to older therapies.

Step-by-Step Solution

Diagnose the patient's acute condition based on clinical presentation and laboratory findings.

The patient has an initial episode of non-fulminant Clostridioides difficile infection (CDI), evidenced by characteristic symptoms, recent antibiotic exposure, and a positive stool immunoassay.

Establishing the severity and distinguishing between an initial episode versus recurrence is necessary to select the correct guideline-directed pharmacotherapy.

Determine the most appropriate first-line pharmacotherapy for this specific diagnosis.

Oral fidaxomicin (or oral vancomycin) is selected to target the intraluminal infection.

Current guidelines recommend oral fidaxomicin as a preferred first-line agent because it is a narrow-spectrum macrocyclic antibiotic that effectively eradicates C. difficile while preserving the normal colonic flora, thereby reducing recurrence rates.

Key Concept

The first-line management for an initial episode of non-fulminant Clostridioides difficile infection is oral fidaxomicin or oral vancomycin. Systemic (intravenous) vancomycin does not reach therapeutic concentrations in the colon and is ineffective for this condition.

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